Groundwater chemistry baseline of the Walloon coal measures in the Clarence-Moreton and Surat basins, Queensland, Australia

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International Association of Hydrogeologists
The Walloon Coal Measures (WCM) are a major target for coal seam gas exploration in the Surat and Clarence-Moreton basins in Queensland and New South Wales, Australia. It is now widely acknowledged that an improved understanding of the groundwater baseline is essential. Fundamental is determining the geological framework and an unbiased examination of the natural range, or baseline, of groundwater chemistry of the coal seams and adjacent aquifers. In order to determine the processes that control the spatial variability and evolution of groundwater chemistry, the chemistry baseline data of the WCM for the Surat and Clarence-Moreton basins are placed within the framework of a 3D geological model. In the assessment of the water chemistry baseline, four groundwater chemistry groups were identified from the hierarchical cluster analysis (HCA) which was applied to historical groundwater chemistry records from the Department of Natural Resources and Mines (DNRM) groundwater database. Each of these distinct groups contains groundwaters of a similar composition, which result from a number of different processes (e.g. groundwater recharge or interaction with other aquifers). However, groundwater of only one group has the typical composition of CSG waters, as documented by very high HCO3, and simultaneously low SO4, Ca and Mg concentrations, whereas the chemical composition of groundwater assigned to the other groups suggests that these follow a different evolutionary pathway. Following this initial screening, a total of ~60 samples was collected from the different groundwater chemistry groups for analysis of water chemistry (major, trace, rare earth elements and dissolved gases) and isotopic fingerprinting (d2H, d2H-CH4, d13C-DIC, d13C-CH4, d18O, 87Sr/86Sr,14CDIC and 36Cl/Cl). The analyses were combined with results from a similar groundwater chemistry study undertaken in the Surat Basin during 2009-2011 that aimed to establish a groundwater chemistry baseline for geological storage of CO2. The analyses of dissolved gases shows that there is a strong variability of dissolved CH4 concentration within groundwaters of the WCM, ranging from values below the reporting limit to ~50 mg/L. Likewise, isotope signatures and groundwater residence times within these coal-bearing sequence are highly variable spatially, reflecting the range of processes involved in groundwater evolution as well as the variable composition of these sedimentary rocks.
Coal mining, Queensland, Australia, Ground water, Aquifers, Simulation, Magnesium, Sedimentary rocks, Isotopes
Raiber, M., Cox, M.,E., Cendón, D. I., & Feitz, A. J. (2013). Groundwater chemistry baseline of the Walloon coal measures in the Clarence-Moreton and Surat basins, Queensland, Australia. Paper presented to the IAH 2013, Perth, Australia : "Solving the groundwater challenges of the 21st century", International Association of Hydrogeologists 40th International Conference, Perth, Western Australia, 15-20 September 2013, (pp. 190).